As for the elephant’s oversized cerebellum, I’ve heard it suggested that it’s for controlling the trunk. Elephant trunks are able to manipulate things with extreme dexterity, allowing them to pluck individual leaves, pick up heavy objects, or even paint. Since the cerebellum is known for “smoothing out” fine motor control (basically acting as a giant library of learned reflexes [including cognitive reflexes], as I understand it), it makes sense that elephant cerebellums would become so large as their trunks evolved to act as prehensile appendages.
According to this, the human brain has about 15 billion neurons in the telencephalon (neocortex, etc.), 70 billion in the cerebellum, and 1 billion in the brainstem. So it sounds like we still have much more circuitry dedicated to generalized abstract intelligence than elephants; they just have better dexterity with a more complex appendage than human limbs (minus the fingers but plus a ton of complexly interacting muscles). If we had cerebella closer in size to the elephant’s, all humans would probably be experts in gymnastics, martial arts, painting, and playing musical instruments.
The “cerebellum is for fine motor control” it now long out of date and has been decisively disproven—i’m not going to link all the relevant articles to back that up in this comment—but will in a future update to an earlier brain architecture post.
The cerebellum is compartmentalized into feed-forward modules that are not much connected to each other, but instead are tightly connected to corresponding cortical regions through thalamic relay, and thus also to corresponding basal ganglia regions (and perhaps more).
The cerebellum is crucially involved in nearly everything the cortex does, as the two are not even functionally distinct, and in general the brain is best understand as a collection of tightly coupled BG-thalamic-cortex-cerebellum recurrent processing modules, each of which has different types of cross local connectivity across modules in the different brain structures the loops traverse.
While fine motor control is certainly far from all that the cerebellum does, it is also certainly something that it does really do (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4347949/). From my understanding, it learns to smooth out motor trajectories (as well as generalized trajectories in cortical processing) using feed-forward circuitry (with feedback of error signals from the inferior olive acting as just a training signal), which is why I called it “learned reflexes”. And, as you mentioned, this feed-forward “reflexive” trajectory-smoothing extends to all cognitive processes.
I have come to see the basal ganglia as helping to decide what actions to take (or where information is routed to), while the cerebellum handles more how the actions are carried out (or how to adjust the information transferred between cortical regions). And it has all the computational universality of extremely wide feed-forward neural networks (https://arxiv.org/abs/1709.02540) due to its huge number of neurons. Maybe this would play into your idea in your other comment about how cerebellar outputs might also help train the cortex.
Actually I think it’s unclear if the cerebellum does anything on it’s own—even motor control, because as explained above from a connectivity standpoint it doesn’t even make sense to talk about cerebellum outside of tightly coupled cortical-cerebellar-BG-thalami loop modules—those are the actual functional connectivity modules of the brain. The brain is essentially a large society of those modules. Humans lacking a cerebellum (or even with sudden cerebellum damage) do not completely lack any specific motor function, but instead show a wide range of mental deficits. But humans lacking motor cortex do show motor deficits (from what I recall).
However, the cerebellum as training/reversion module theories do generally predict that the cerebellum is much more important for motor vs sensor cortex, just due to the nature of the sensor → latent → motor process which is compressive (and thus mostly UL based) in the first stage and then expansive (and thus mostly RL based) in the latter stage. And those theories specifically correctly predict lack of cerebellum mapping in earliest sensor cortex (as there is no need to send training signal to retina) - which is exactly what you find. Other theories do not make these specific correct testable predictions.
That being said yes agreed it probably “learns to smooth out motor trajectories” probably as a subset of learning to backdrop fine grain credit assignment through time for the cortex. (much more important for motor than sensor).
And yes agreed on the BG role.
As for ‘huge number of neurons’ - this is a red herring. The unit of computation is the synapse, not the neuron. The tiny granule cells only have 3-4 synapses each, and it’s pretty clear they are doing some decompression/recoding of incoming channel/bandwidth constrained signals. Regardless their contribution to total compute power is minor—not even in the trillions of synapses.
As for the elephant’s oversized cerebellum, I’ve heard it suggested that it’s for controlling the trunk. Elephant trunks are able to manipulate things with extreme dexterity, allowing them to pluck individual leaves, pick up heavy objects, or even paint. Since the cerebellum is known for “smoothing out” fine motor control (basically acting as a giant library of learned reflexes [including cognitive reflexes], as I understand it), it makes sense that elephant cerebellums would become so large as their trunks evolved to act as prehensile appendages.
According to this, the human brain has about 15 billion neurons in the telencephalon (neocortex, etc.), 70 billion in the cerebellum, and 1 billion in the brainstem. So it sounds like we still have much more circuitry dedicated to generalized abstract intelligence than elephants; they just have better dexterity with a more complex appendage than human limbs (minus the fingers but plus a ton of complexly interacting muscles). If we had cerebella closer in size to the elephant’s, all humans would probably be experts in gymnastics, martial arts, painting, and playing musical instruments.
The “cerebellum is for fine motor control” it now long out of date and has been decisively disproven—i’m not going to link all the relevant articles to back that up in this comment—but will in a future update to an earlier brain architecture post.
The cerebellum is compartmentalized into feed-forward modules that are not much connected to each other, but instead are tightly connected to corresponding cortical regions through thalamic relay, and thus also to corresponding basal ganglia regions (and perhaps more).
The cerebellum is crucially involved in nearly everything the cortex does, as the two are not even functionally distinct, and in general the brain is best understand as a collection of tightly coupled BG-thalamic-cortex-cerebellum recurrent processing modules, each of which has different types of cross local connectivity across modules in the different brain structures the loops traverse.
While fine motor control is certainly far from all that the cerebellum does, it is also certainly something that it does really do (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4347949/). From my understanding, it learns to smooth out motor trajectories (as well as generalized trajectories in cortical processing) using feed-forward circuitry (with feedback of error signals from the inferior olive acting as just a training signal), which is why I called it “learned reflexes”. And, as you mentioned, this feed-forward “reflexive” trajectory-smoothing extends to all cognitive processes.
I have come to see the basal ganglia as helping to decide what actions to take (or where information is routed to), while the cerebellum handles more how the actions are carried out (or how to adjust the information transferred between cortical regions). And it has all the computational universality of extremely wide feed-forward neural networks (https://arxiv.org/abs/1709.02540) due to its huge number of neurons. Maybe this would play into your idea in your other comment about how cerebellar outputs might also help train the cortex.
Actually I think it’s unclear if the cerebellum does anything on it’s own—even motor control, because as explained above from a connectivity standpoint it doesn’t even make sense to talk about cerebellum outside of tightly coupled cortical-cerebellar-BG-thalami loop modules—those are the actual functional connectivity modules of the brain. The brain is essentially a large society of those modules. Humans lacking a cerebellum (or even with sudden cerebellum damage) do not completely lack any specific motor function, but instead show a wide range of mental deficits. But humans lacking motor cortex do show motor deficits (from what I recall).
However, the cerebellum as training/reversion module theories do generally predict that the cerebellum is much more important for motor vs sensor cortex, just due to the nature of the sensor → latent → motor process which is compressive (and thus mostly UL based) in the first stage and then expansive (and thus mostly RL based) in the latter stage. And those theories specifically correctly predict lack of cerebellum mapping in earliest sensor cortex (as there is no need to send training signal to retina) - which is exactly what you find. Other theories do not make these specific correct testable predictions.
That being said yes agreed it probably “learns to smooth out motor trajectories” probably as a subset of learning to backdrop fine grain credit assignment through time for the cortex. (much more important for motor than sensor).
And yes agreed on the BG role.
As for ‘huge number of neurons’ - this is a red herring. The unit of computation is the synapse, not the neuron. The tiny granule cells only have 3-4 synapses each, and it’s pretty clear they are doing some decompression/recoding of incoming channel/bandwidth constrained signals. Regardless their contribution to total compute power is minor—not even in the trillions of synapses.